The best way to stencil is find 3 or 4 animal stencils that you love. They will need to be big enough that you can see them from across the room. I would say about 12” X 12”. Once you have found the stencils then you need to decide on the colors of the room. here are your choices. you can pick 2 colors if you  are doing 4 stencils and then make 2 animals the same color and the other two animals the other color. But my favorite way to do this is picking 3 animal and choosing 3 different shades of the same color. this should not cost a lot as I have even seen stencils at the dollar store at time and then it is 3 quarts of paint.
The next big decision is to decide where the stencils are going to look best in the room. You could choose over the bed, around the room, or at the top of the wall. When I did this for my sons room I choose at the exact middle of his room ( where a chair rail would go.)  My idea was to give it some color and go with the theme of his bedding with out is being over whelming. There are a couple steps to making sure that this will turn out great –
Step #1 Start under the light switch
Step #2 Tape the stencil #1 in place and then #2 and 3 following
Step #3 Use a paint brush that is like a sponge
Step #4 Don’t use to much paint
Step #5 Take off the stencil before is dries all the way
Step #6 Repeat
This should get you pointed in the right direction for making your free animal wall paper – (With out the wall paper)